The present invention is directed to a tool bit for insertion into a tool bit chuck in a manually operated tool used for chiseling and/or percussion drilling and includes an axially extending chucking shank having at least two rotary entrainment grooves open at the end of the shank inserted into the tool bit chuck. Each rotary entrainment groove has an entrainment side flank with such flanks located diametrically opposite one another. In addition, the shank has at least one locking groove closed at its ends extending transversely of the axial direction and located between the rotary entrainment grooves.
Tool bits for manually operated tools are disclosed in DE-PS 25 51 125 with the chucking shanks of such tool bits having at least one locking groove closed at its end extending transversely of the axial direction along with two rotary entrainment grooves open at the end of the shank inserted into the chuck. The tool bit chuck for the tool bit has at least one radially displaceable locking element in the shape of a sphere or ball or possibly in the shape of a roller. A positively locked connection between the tool bit and the chuck in the axial direction is established by the cooperation of the locking element with the locking groove.
This positive connection serves to assure that the tool bit is secured in the tool bit chuck. Neither the locking groove nor the locking element is exposed to particularly high stresses in the manner in which the shank is held in the chuck. Larger stresses could arise if the tool bit must be pulled out of a bore in a structural member by means of the hand-held tool when under some circumstances forces due to jamming or seizing phenomena must be overcome. In such cases excessive stresses can occasionally occur when the tool bit is pulled out of the chuck in an undesirable manner. Greater problems are experienced in the known tool bit when, based on the torque to be transmitted, premature wear of the shank occurs. Such problems tend to increase, since the trend is to provide manually operated tools with increased output for enabling the utilization of drilling tool bits of the greater diameter. Under such circumstances the torque to be transmitted is so high that the available surface of the entrainment-side flanks of the rotary entrainment grooves are too small with the result that high specific surface pressure develops and a premature failure of the tool bit occurs due to wear. This failure of the chucking shank due to wear generally occurs prior to the normal wear of the working region of the tool bit under normal use. Thus the economy of such very expensive tool bits is especially questioned.